A new bridge is under construction to carry five northbound lanes of Interstate-680 across the Carquinez Straight near the cities of Benicia and Martinez in northern California. The bridge consists of a haunched prestressed lightweight concrete single cell box girder. The total length of this 16 span bridge is 7432 ft and its typical width is 82.2 ft. The main span is 659 ft long, a record for lightweight concrete. Twelve spans are being constructed segmentally using the balanced cantilever method. Approach structures, which were constructed on falsework, are provided at both ends of the bridge.

Besides normal highway traffic, the bridge is designed to carry light rail vehicles. The bridge is located in a seismically active area and is being designed for the highest level of seismic performance considered by Caltrans. In addition, ship collision is a major design issue in this heavily traveled marine waterway.

Piers for the main structure are made up of four octagon shaped columns that are tied together with full height connecting walls. Careful consideration has been given to the superstructure-pier connections to assure that all forces generated in an earthquake can be transferred without damage to these joints.

Each of the deep-water pier foundations must resist large earthquake and ship collision loads. They are made up of eight or nine 8.2 ft diameter cast-in-drilled hole piles terminating in large prestressed concrete pile caps near the water surface. The pile-to-pile cap connection provides for full moment transfer. Piles pass through approximately 40 feet of water and 100 of mud before encountering relatively weak rock. These piles have composite stay-in-place steel casings that project into the underlying rock a sufficient distance to prevent damage to the pile rock socket during a large earthquake. Large diameter (7.2 feet) rock sockets up to 113 feet long below the steel casing are provided at each pile to resist the large axial tension and compression forces that will be developed.

NRV Principal, Charles Redfield, played a key role in developing the preliminary design concept. He also was instrumental in the final design of the superstructure, while NRV Principal, Richard Nutt helped develop seismic design criteria, designed the deep water pile foundations, and assisted with other aspects of the design of the substructure and approach spans. Both Mr. Redfield and Mr. Nutt provided construction support and were instrumental in developing solutions to difficult field problems.